1. Field of the Invention
The invention relates to a process for preparing silicone-modified polymers in the form of their aqueous polymer dispersions or in the form of their polymer powders, to their use, and to protective colloids comprising silicone units.
2. Description of the Related Art
Organosilicon compounds such as organosiloxane polymers are used for hydrophobicizing polymers of ethylenically unsaturated monomers. Such hydrophobically modified polymers are used in many fields in the form of their polymer powders, in particular water-redispersible polymer powders, or as aqueous polymer dispersions. They are employed as binders in coating compositions or adhesives, in particular in the building sector and textile sector, and also as binders in cosmetics and haircare products.
It is known from WO-A 95/20626 that water-redispersible polymer powders can be modified by addition of noncopolymerizable organosilicon compounds. EP-A 0352339 describes protective surface coatings for concrete constructions, which comprise copolymers of divinylpolydimethylsiloxane with acrylate esters or methacrylate esters and with vinyl- or acryl-functional alkoxysilanes as a solution in organic solvent. EP-B 771826 describes aqueous binders for coatings and adhesives which are based on emulsion polymers of vinyl esters, acrylic or methacrylic esters or vinyl aromatics containing polysiloxanes having unsaturated radicals, for example vinyl, acryloxy or methacryloxy groups, as crosslinkers. EP-A 943634 describes aqueous latices for use as coating compositions, which are prepared by copolymerization of ethylenically unsaturated monomers in the presence of a silicone resin containing silanol groups. EP-A 1095953 describes silicone-grafted vinyl copolymers in which a carbosiloxane dendrimer is grafted onto the vinyl polymer.
It is known from DE-A 19951877 and WO-A 99/04750 that silicone-containing polymers are obtainable by polymerization of ethylenically unsaturated monomers in the presence of a linear polydialkylsiloxane having polyalkylene oxide side chains. US-A 5216070 describes a process for the inverse emulsion polymerization of carboxyl-functional monomers, in which linear polydialkylsiloxanes having polyalkylene oxide side chains are used as an emulsifier.
DE-A 4240108 describes a polymerization process for preparing polysiloxane-containing binders for use in dirt-repellent coatings, in which the monomers are polymerized in the presence of an OH—, COOH— or epoxy-functional polydialkylsiloxane which may additionally contain polyether groups. DE-A 10041163 discloses a process for producing hair-cosmetic formulations, in which vinyl esters are polymerized in the presence of a polyether-containing compound, for example polyether-containing silicone compounds.
A disadvantage of the silicone-modified emulsion polymers described in the prior art is a strong tendency to hydrolyze and to undergo uncontrolled crosslinking, which in some applications may indeed be desirable and is subsequently reinforced by addition of silane and catalyst, but in the case of surface coating dispersions or when the emulsion polymers are used as coating compositions leads to undesirable gel particles, “specks” and insoluble constituents. Furthermore, the silicone-containing emulsion polymers known hitherto are often not alkali-resistant, since silicones are known to be unstable in an alkaline medium. For this reason, the hydrophobicity and the associated positive properties of the systems described hitherto decrease greatly after a prolonged period of time. Finally, the introduction of a large amount of silanes or silicones into the emulsion polymers results in establishment of an unsatisfactory particle size distribution, i.e. the particles become too large and the polymer becomes inhomogeneous, which can lead to serum formation or phase separation. Furthermore, coagulum formation can also occur.